Semi-conductive device and method of producing same



July 22, 1958 c. VAN VESSEM &

SEMI-CONDUCTIVE DEVICE AND METHOD OF PRODUCING SAME I Filed May 16, 1955 INVENTOR OENRAAD VAN VESSEM United States Patent O SEMI-CONDUCTIVE DEVICEAND METHOD OF PRODUCING SAME Jan Coenraad' van Vessem, Eindhoven, Netherlands, as-

signor, by mese assignnents, to North American Philips Company, Inc., New York, N. Y., a Corporation of Delaware Application May 16, 1955,. Serial No. 508,661

Clains priority, application Netherlands May 18, 1954 7 Claims. (Cl. 317-234) This. invention relates to semi-conductive devices, and in particular to transistors of the junction type having a well or recess in the semi-conductive member to accommodate an electrode, and to a method for producing such a transistor.

In transistors of the foregoing type, a recess is provided in at least one of the surfaces of the semi-conductive member, and electrode material is disposed in the recess and subsequently alloyed with the underlying semiconductive member. In some cases, two such recesses and electrodes are arranged on opposite surfaces. This construction is for the purpose of producting a low base resistance; A particular constructionis completely described in detal in R. C. A. Review, Volume XIV, No 4, pages 586-598'. (1953).

In the manufacture of such devices, in particular, transistors, the difiiculty is found that the electrode material disposed in the well or recess tends to creep up the walls of the recess with the result that the fa'vorable shape of the electrode desired, namely, the planar juncp tion, is not obtained.

The Chief object of the invention is to provide a simple method and construction by wlfich this ditliculty is avoided in the manufacture of devices or electrode systems of the type described in the above-noted publication.

According to the invention, the electrode material is accommodated in an insulating tube, which in turn is arranged coaxially in the recess, and the material then united or alloyed to the semi-conductive member by heating, the confined electrode material thus being prevented from spreading. The tube preferably consists of refractory material, such as, for example, quartz. The term "refractory material" as used in this latter connection is to be understood to mean a material which does not change its characteristcs to a perceptible degree at the temperature at which the electrode material is alloyed to the semi-conductive member, which temperature may, for example, be about 500" C. or less. As an alternative, it is also possible for the tube to be made from a materal which at the above heating or alloying temperature is decomposed in whole or in part. Such a material is, for example, an organic synthetic resin, such as a silicone resn. The use of the latter substance may have the advantage that the tube, When thus eliminated, will not give rise to mechanical stresses and disturbances in the crystal lattice during solidification of the electrode material. If a current supply wire is to be soldered to the alloyed electrode, it is preferably eifected at a stage at which the insulating tube still surrounds the electrode material. Thus, there is substantially no likelihood of disperson or spreading of the electrode material during solidfication.

The invention will now be described with reference to the accompanying drawing, in which:

Fgs. 1 to 4 are cross-sectional views of several forms of transistors in accordance with the invention;

2,844,770 Patented July 22, 1958 Fig; 5 shows. an insulating tube filled with electrode material.

Referring now to the figures, the transistors shown each consist ofa semi-conductive'member 1, for example, a disc'of germanium approximately microns thick cut from' a monocrystal; In the construction shown in Figs. 1 to 3, a recess or well 2 is formed in the surface of this member. Such a recess can' be produced by etching or boring, In the construction shown in Fig. 4, two recesses 2 and 3 are formed one on each side of the member 1.

In each recess, an electrode 4' is Secured to the semiconductve member 1 by alloying. For this purpose, a suitable electrode metal 5, for example, indium if the semi-conductive member consists of n-type germanium, or a lead' alloy` containing antimony if p-type germanium is used, is disposed in an insulating tube 6 Fig. 5). As is well known, the electrode material when alloyed with the semi-conductive member alters its conductivity in a predetermined manner, e. g., by changing the conductivity type of a portion of the semi-conductive member to establish a rectifying or p-n junction theren. Where the electrode material is of substantial size, a large-area junction is generally produced. Next, the tube 6 is sawed into lengths as is shown dia'grammatically by arrows, preferably lengths of a= size suchthat each of them contains a suitable supply of metal. If the size is too large, the metal will tend to`fiow out at' the bottom of the tube and to creep up the walls of' therecess 2 when it is alloyed to the semi-conductive member. If the size is too short, it Will b'e dificult to secure a current conductor to the electrode by soldering; -The correct size can be ascertained experimentally, while at the same time allowance is made for the materials used which according to their nature will assist in the disperson of the electrode to a larger or lesser extent. The diameter of the electrode might be 0.4 mm. and its height 1 mm., it may be constituted by indium. However, a slight amount of spreading as is shown in Fig. 2, need not always present difiiculties. Finally, the metal-filled tube 6 is placed in the recess 2 With the metal facng the bottom, and heat applied to cause the confined metal 5 to alloy to the underlying portion of the semi-conductive member 1.

The tube 6 may consist of refractory insulating material, for example, quartz glass or sintered quartz. In this event, it will continue to surround the electrode 4 after alloying, but may, if required, subsequently be removed by etching. As an alternative, use may be made of a tube consistng of a non-refractory material, for example, an organic substance, which may, for example, be carbonised during alloying and thus may retain sufficient coherence for preventing the disperson of the electrode metal. Examples of such materials are Teflon. A similar result can be obtained by using a combination of an organic binder and a refractory filler. The use of such a temporary insulating tube is indicated at 7 by broken lines in Fig. 3. When the tube has been removed, as shown in Fig. 3 the resultant alloy electrode 4 possesses a substantially rod-like shape and s spaced from the walls of the semi-conductive member 1 defining the recess 2. When the tube 6, as shown, is cylindrical, then the red-like electrode 4 will also be of the same cylindrical shape. An example of the combination of organic binder and refractory filler is a mixture of Tefion and silica. As has been mentioned hereinbefore, the use of such a removable tube may be of advantage if mechancal stresses have to be avoided as far as possible during cooling. If a refractory tube is used, these stresses can also be reduced by applying a layer of graphite or a similar soft material to the inner wall of the tube. In the construction shown in Figures 1 to 3, a second electrode 8 is arranged on the plane surface of the semi-conductive member opposite the electrode 4. This second electrode 8 may also be arranged in a recess, as is shown in Fig. 4, in which event a tube 6 may be used to preventidispersion or spreading of the electrode materiah Anohmic base connection 12 is also shown in the figures. i

The electrodes 4 and 8 have current supply wires 9 and 10 secured to them by soldering. As has been mentioned herenbefore, in the constructions' in which this tube 7 (Fig. 3) is removed, this soldering process is preferably performed prior to the tube being removed. The remaining constructional details of the transistors illustrated in the drawing may be found in the abovenoted publication.

While I have described myinvention in connection with specific embodiments and applications, other modifications thereof will be readily apparent to those skilled in this art without departing from the spirit and scope of the invention as defined in the appended claims.

What is claimed is:

1. A method of producing a semi conductive device comprising a semi-conductve member having a recess in a surface portion thereof, comprising providing electrode material capable of alteringthe conductivity of said semi-conductve member when alloyed thereto in a holiow, insuiatng member, dsposing said hollow member in the recess with the electrode material exposed to and facing the portion of` the semi-conductive member at the bottom of the recess, and therefater alloying said electrode material to the semi-conductive member by applying heat thereto while the electrode material is confined by the hollow member. 4

2. A method as claimed in claim 1 in which the hollow member comprises a tube consisting essentially of refractory, insulating material.

3. A method as claimed in claim 2 in which the tube is removed after the electrode material has been alloyed to the sem-conductive member.

4. A method as claimed in claim 1 in which the hollow member is a tube consisting essentially of nonrefractory, heat-decomposable material and is decomposed at least in part during the alloying of the electrode.

5. A semi-conductive device comprsng a semi-conductive member having a recess in a surface portion thei-cof, and an electrode arranged in said recess and alloyed to the semi-conductive member to alter a portion of the conductivity thereof, said electrode haw'ng an elongated portion spaced from the walls of the semiconductve member defining the recess.

6. Anelectrode system comprising a semi-conductive body having at least one recess in a surface portion thereof, and an electrode in said recess and alloyed to the body and forming a substantally large-area, rectifying junction, a portion of said electrode being substantally rod-shaped and being spaced from the semi-conductive member and not being dispersed during the alloying.

7. An electrode system comprisng a semi-conductive body having a recess in a surface portion thereof, and

4 an electrode in said recess and alloyed to the body to form a p-n junction therein, substantiaily all of said electrode having a cylindrical, red-like shape.

References Cited in the file of this patent UNITED STATES PATENTS 2,612,567 Steutzer Sept. 30, 1952 2,717,341 North Sept. 6, 1955 

